Kaolinite or kaolin is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra. Rocks that are rich in kaolinite are known as china clay, white clay, or kaolin.
The largest use for kaolin is in the production of paper, including ensuring the gloss on some grades of paper. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.
Kaolin that is well suited as a raw material in the preparation of the compounds of the present invention have the following analysis:
IngredientsWeight %Whiteness (L value)95Moisture (max. %)1.0LPH (20% solids)4.2-5.2Median Particle Size (microns)0.6Oil Absorption40Wet Screen Residue (% +325 mesh)<0.03Index of Retraction1.56Specific Gravity2.58Bulking Value (lb/solid gallon)21.66Brightness (%)88
Kaolin is insoluble and has excellent absorbent qualities. These qualities are used to draw out impurities and toxins and thereby clears the skin of excess oil, dirt, pollutions and other waste materials. Apart from this, it forms a stable basis for skin masques and can be used on any type of skin.
The cosmetic use of kaolin has been based primarily on its insolubility and ability to absorb water. We on the other hand are interested in the use of kaolin that has been surface treated with a particular type of silicone that can be easily dispersed in oils and can provide water proofing films to skin.
There are many areas in which waterproofing is highly prized. This includes sun care applications, pigmented products and many others where wash off is frowned upon by the consumer. Surface treating the kaolin result in a kaolin that is (a) less dusty when handled, (b) more flowable, (c) has better dispersibility in oils and in emulsion, resulting in less whitening when applied to skin and improved waterproofing when applied to skin, (d) has better stability in emulsions when dispersed in oils because of the durability of the surface treatment.
Surface treated kaolin also can be used to modify cosmetic powders providing enhanced spreadability and improved cosmetic elegance.
Kaolin has very reactive sites. U.S. Pat. No. 6,071,335, incorporated herein by reference, to Braggs issued Jun. 6, 2000 teaches “A method for modifying the surface of kaolinite or a kindred mineral comprises the step of subjecting the mineral to a water vapor plasma. The modification involves the generation of reactive hydroxyl sites on the surface of the kaolinite. The plasma treatment may be followed by treatment with an appropriate chemical reagent to further modify the surface properties of the mineral.”
'335 teaches “Kaolin is a common mineral. It is a member of the clay mineral group of phyllosilicates which group also includes talc (or soapstone) and pyrophyllite. Clay minerals similar to kaolinite include dickite, nacrite, anauxite, halloysite, montmorillonite (dominant clay in bentonite), beidellite, nontronite, hectorite, saponite, and illite. Clay minerals similar to talc include minnesotaite.
Kaolin has a wide variety of applications in industry, particularly as a paper filler and a coating pigment. It is used as an extender in aqueous based paints and ink, a functional additive in polymers and is the major component in ceramics. Kaolin is an inexpensive additive, which can improve the properties of the material in which it is dispersed, provided it is able to form stable dispersions. In order to achieve this the surface is usually modified in some way so as to enhance colloid stability in a system whether it be organic, as for polymers, or in aqueous dispersions.
The surface of kaolin, like other clay minerals, is relatively inert, unlike silica and many other minerals. Kaolin has two different basal cleavage faces. One face consists of a siloxane surface with very inert —Si—O—Si— links. The other basal surface consists of an octahedral, gibbsite [Al(OH)3] sheet. Both of these surfaces are theoretically electrically neutral. At the edges of a platelet and at the surface ridges the lattice is disrupted and broken bonds occur which are accommodated as OH groups. These edges have been estimated to occupy approximately 10% of the whole kaolinite surface.
The hydroxyl groups at the plate edges are considered to be the major reactive sites of clay surfaces including kaolin. Sometimes these groups are porpoxylated by reaction with propylene oxide. This quenches the reactivity but provides little in the alteration of the properties of the clay viz-a-viz dispersibility in oils.
As will become apparent, our approach is to use a reactive silicone with kaolin to not only quench the reactive groups but also to incorporate a variety of groups that are either silicone soluble (siliphillic), fluoro soluble (fluorophillic) or oil soluble (oleophillic). This results in materials that allow for a thin, transparent kaolin film that provides a number of advantageous not present in currently existing products including (a) less dusty when handled, (b) more flowable, (c) has better dispersibility in oils and in emulsion, resulting in less whitening when applied to skin and improved waterproofing values when applied to skin, (d) has better stability in emulsions when dispersed in oils because of the durability of the surface treatment.